1. Field of the Invention
The present invention relates to a method of measuring an object by employing an imaging means that is adapted to measure a length and the like of the object by utilizing data on the overall shape and dimension of the object. The present invention also relates to an apparatus for the method.
2. Related Art Statement
An apparatus for measuring a dimension of an object (i.e., the object whose image is obtained for observation) by employing an endoscope is disclosed in Japanese Patent Laid-Open (kokai) No. 59-70903. In the disclosed art, in order to measure a length of an object, the apparatus must include a laser beam generating means for projecting a reference length, necessary to the length measurement, onto the object, as well as a light guide for guiding the laser beam through the endoscope, and a lens for projecting the beam. In addition, the art has a drawback in that the structure of the endoscope is complicated, requiring its front end portion to have a large diameter, and precluding the front end from being inserted into a hole with a small diameter. Also, the art involves a certain limitation of the measurement condition; a length cannot precisely be measured if the portion onto which the laser beam is projected is not a planar surface perpendicular to the laser beam.
In view of these disadvantages, the present inventor has proposed, in U.S. Pat. No. 4,989,083, a method of measuring the length or the like of a particular portion of an object which is to be examined. In the method, an imaging means such as an electronic endoscope or a small TV camera is employed to obtain an image of an object whose overall shape and dimension are already known. On the other hand, a perspective of the object is drawn by computer graphics on the basis of data on the known shape and dimension of the object. Certain parameters for drawing the perspective are varied with a view to making the perspective coincident with the image of the object, and thus to allowing for the measurement of the length, etc.
The proposed method (hereinafter referred to as "the previous proposal") requires the process of making the image of the object and the perspective of the object coincident with each other by, for instance, superimposing them. This matching (e.g., superimposing) process is executed by varying, on three-dimensional coordinates, six parameters, namely, positions x, y and z and directions .theta.x, .theta.y, and .theta.z of the graphic form of the object, such as those shown in FIGS. 23 and 24. In the previous proposal, these parameters are varied through the operator's operation on the keyboard so as to superimpose the image of the object and the corresponding graphic form on each other. However, since this operation is very complicated, such a superimposing operation cannot easily be performed even by a very skilled operator.